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Size effects in shear force design of concrete beams

Althin, Axel LU and Lippe, Mårten LU (2018) In TVBK-5265 VBKM01 20181
Division of Structural Engingeering
Abstract
Shear failures in reinforced concrete beams are complex problems that depend on many different mechanisms, such as aggregate interlock and dowel effect. This makes the prediction of shear failures difficult as they are not strictly tied to the material and depend on other factors including the size of the beam. In particular the height of the concrete cross section plays a role in the amount of shear stress the beam can carry. This effect is appropriately named the size effect, and is not well defined for smaller concrete beams, which is why
they are studied in this master thesis.
The main objective of this report is to determine if the size effect is present in smaller reinforced concrete beams as well as examining the accuracy of the... (More)
Shear failures in reinforced concrete beams are complex problems that depend on many different mechanisms, such as aggregate interlock and dowel effect. This makes the prediction of shear failures difficult as they are not strictly tied to the material and depend on other factors including the size of the beam. In particular the height of the concrete cross section plays a role in the amount of shear stress the beam can carry. This effect is appropriately named the size effect, and is not well defined for smaller concrete beams, which is why
they are studied in this master thesis.
The main objective of this report is to determine if the size effect is present in smaller reinforced concrete beams as well as examining the accuracy of the Eurocode formulas when determining shear failures for smaller concrete beams. The study consists of a theoretical part where the Eurocode is studied along with the mechanisms of shear failure as well as a practical part where concrete beams were cast and tested. In the laboratory beams the conditions, aside from height, were held as constant as possible in order to limit the other factors, thus giving a more accurate representation of the size effect. Both beams with and without shear reinforcement were studied.
The experimental results showed that a size effect is present in the smaller reinforced concrete beams, both shear reinforced and unreinforced, as the stresses at failure decreased in the beams as the height increased. Because the other known factors for shear failure were kept mostly constant, the conclusion is that the size effect contributed to the variation of stress at failure for the different beams. Regarding the Eurocode formulas, differences could be seen between the calculated theoretical shear capacity and the laboratory shear capacity. The theoretical values for shear reinforced concrete beams were closer to the
laboratory values than the unreinforced beams, though the reason for this is unknown. The theoretical values were always on the safe side for all the tested beams. (Less)
Popular Abstract
If the strength of the material was the only factor affecting concrete beams they would all fail at the same stress, as long as the same quality concrete is used. Why is it then that a larger concrete beam generally fails at a lower stress than a smaller beam? Due to a phenomenon known as the size effect.
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author
Althin, Axel LU and Lippe, Mårten LU
supervisor
organization
course
VBKM01 20181
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
reinforced concrete, shear force, size effect, small beams
publication/series
TVBK-5265
report number
TVBK-5265
ISSN
0349-4969
language
English
additional info
Examinator: Annika Mårtensson
id
8944751
date added to LUP
2018-06-08 10:19:56
date last changed
2018-06-08 10:19:56
@misc{8944751,
  abstract     = {Shear failures in reinforced concrete beams are complex problems that depend on many different mechanisms, such as aggregate interlock and dowel effect. This makes the prediction of shear failures difficult as they are not strictly tied to the material and depend on other factors including the size of the beam. In particular the height of the concrete cross section plays a role in the amount of shear stress the beam can carry. This effect is appropriately named the size effect, and is not well defined for smaller concrete beams, which is why
they are studied in this master thesis.
The main objective of this report is to determine if the size effect is present in smaller reinforced concrete beams as well as examining the accuracy of the Eurocode formulas when determining shear failures for smaller concrete beams. The study consists of a theoretical part where the Eurocode is studied along with the mechanisms of shear failure as well as a practical part where concrete beams were cast and tested. In the laboratory beams the conditions, aside from height, were held as constant as possible in order to limit the other factors, thus giving a more accurate representation of the size effect. Both beams with and without shear reinforcement were studied.
The experimental results showed that a size effect is present in the smaller reinforced concrete beams, both shear reinforced and unreinforced, as the stresses at failure decreased in the beams as the height increased. Because the other known factors for shear failure were kept mostly constant, the conclusion is that the size effect contributed to the variation of stress at failure for the different beams. Regarding the Eurocode formulas, differences could be seen between the calculated theoretical shear capacity and the laboratory shear capacity. The theoretical values for shear reinforced concrete beams were closer to the
laboratory values than the unreinforced beams, though the reason for this is unknown. The theoretical values were always on the safe side for all the tested beams.},
  author       = {Althin, Axel and Lippe, Mårten},
  issn         = {0349-4969},
  keyword      = {reinforced concrete,shear force,size effect,small beams},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVBK-5265},
  title        = {Size effects in shear force design of concrete beams},
  year         = {2018},
}